1. Field of the Invention
This invention is in the field of joining waste or drain pipe, more particularly, in the field of joining plain ended waste pipe installed mainly in buildings above ground although the coupling can also be used underground.
2. Description of the Prior Art
For many years the production of cast iron soil pipe made use of sand molds. Both pipe and fittings were produced in such molds to tolerances compatible with the process. Of late, most soil pipe are cast in metal molds where tolerances of a closer nature can be maintained. However, since both processes are in practice, it is necessary to maintain a rather wide tolerance between the maximum and the minimum outside diameter of soil pipe and fittings. Also, since these products must be joined together in a leak free system, the coupling must be compatible with the relatively wide range of dimensions encountered. For instance, one may expect to encounter in a four inch nominal size pipe line outside diameters of 4.44" and 4.32" which must be joined together. A number of sleeve type joining methods have been proposed utilizing a fixed sleeve with a rubber sleeve insert into which are inserted the ends of pipe to be joined. A sleeve of this nature would offer excellent rigidity; however, this type joining method has not been successful due to the relatively wide variation in outside diameters.
Several couplings for joining soil pipe are in commercial use, both patented and unpatented. Probably the most widely used is revealed by Gordon Evans in his U.S. Pat. No. 3,233,922. While the Evans device produces a satisfactory joining method under most conditions, it is made up of several specially formed members requiring time consuming assembly. There is also a clamping device known commercially as AKO used for joining plain ended pipe wherein a plain steel strip is formed around a sleeve type rubber gasket. This method utilizes bolts through holes in each end of the strip to clamp the gasket against the outside surfaces of pipe inserted therein. However, this type clamp does not have the ability to seal pipe ends of varying diameter and is used mainly in Europe where tolerances are relatively small. Such a clamp was tested by joining two soil pipe of the same nominal diameter, one of the ends joined being at the minimum tolerance and other at the maximum tolerance. Leakage occurred at a pressure below that considered acceptable. The present invention eliminates the need for complex members and improves the utility of the joining device without giving up its versatility.